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A294379
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Numbers k such that (62*10^k - 197)/9 is prime.
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0
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1, 5, 7, 14, 17, 40, 53, 95, 97, 113, 122, 125, 145, 374, 470, 485, 1685, 5324, 8035, 10745, 52448, 68059
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OFFSET
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1,2
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COMMENTS
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For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 8 followed by the digits 67 is prime (see Example section).
a(23) > 2*10^5.
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LINKS
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EXAMPLE
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5 is in this sequence because (62*10^5 - 197)/9 = 6263 is prime.
Initial terms and associated primes:
a(1) = 1, 47;
a(2) = 5, 688867;
a(3) = 7, 68888867;
a(4) = 14, 688888888888867;
a(5) = 17, 688888888888888867; etc.
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MATHEMATICA
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Select[Range[1, 100000], PrimeQ[(62*10^# - 197)/9] &]
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CROSSREFS
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KEYWORD
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nonn,more,hard,changed
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AUTHOR
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STATUS
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approved
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